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The present invention relates to imaging systems for electronic components, such as those used in pick and place machines, and more particularly to imaging systems which image a portion of a component onto a linear detector line by line, and are able to provide information about the height of a feature on the component.
Prior art systems for detecting height and coplanarity are typically either vision based or premised on the use of a large array, fixed format detector. In general, these enhanced systems can be divided into two separate groups; those which are based on a linear detector and those which are not (e.g., vision based and large array detectors systems). Vision based and large array detector systems are typically not xe2x80x9con-headxe2x80x9d systems. In on-head sensing systems, a sensor senses the orientation and condition (e.g., coplanar, absence/presence of features, etc.) of the component while the component is transported to the printed circuit board. On-head systems are preferred over other systems because they provide exceptional efficiency in placing the component, leading to a high throughput in the electronic assembly operation. On the other hand, off-head systems have a sensor which senses the orientation and condition of a component while the component is stationary with respect to the printed circuit board. Vision based and large array detector systems have a fairly large weight and size, so as to limit the scanning speed for the sensor in an xe2x80x9con-headxe2x80x9d application.
Linescan sensor systems are characterized by having a linear detector and are adapted to scan a portion of a component. Associated electronics assemble multiple scans of a portion of a component and provide a composite image of the area of interest on a component. However, existing linescan systems are typically off-head which slows down the process of placing the component. Furthermore, many are based on the principle of triangulation (the use of structured light to compute a height), which requires complex optics and registration in the sensor.
The prior art lacks a versatile, compact linescan sensor system reporting coplanarity, component quality and orientation of the object, which system is adapted for use either in xe2x80x9con-headxe2x80x9d or xe2x80x9coff-headxe2x80x9d applications. The ideal system would allow for inspection of features on different types of complex components at high throughput, and be easily adapted for use with pick and place machines, wire bonders and screen printers.
The present invention is a linescan sensor which collects a first assembled image of the component while the component is a first distance away from a first line focus, and then collects a second assembled image of the component at a second distance away from a second line focus. In embodiment A, a sensor alternatively energizes the first line foci and then the second line foci, while a linear detector in the sensor provides a partial image of the same portion of the component resulting from each line foci. In embodiment B, a sensor energizes a single line focus and the sensor scans the component once at a first distance from the component and then at a second distance from the component, a linear detector in the sensor providing partial images of the component during each of the two scans. With each method, the two resulting sets of partial images are assembled into two composite images from which associated electronics compute the height of a feature on the component, such as a ball, lead, column or grid on the scanned surface of the component. Once the height of at least four features on the component is computed, a measure of the coplanarity of the component may be computed. Additionally, the height information from the present invention may be used to assess the quality of a component, such as ascertaining the absence or presence of critical features on the component as a measure of the component quality.
An additional optical path in each embodiment may be present and used with a variety of different types of illumination, so as to optionally provide two dimensional location information. In such case, the partial image resulting from the additional optical path is interleaved with the partial images of either method so as to form a third assembled image of at least a portion of the component.
The method and apparatus of the present invention is useful for both single and multi-nozzle pick and place machines, but may also be used with screen printers to assess whether applied solder bricks are present or absent, or to assess whether the height of the solder bricks is appropriate. Optionally, the method and apparatus of the present invention is useful with wire bonders, to ascertain the height of a bonded wire or the like as a measure of the quality of the bonding process.